Solar cell device

ABSTRACT

A photovoltaic cell including: (a) a housing including an at least partially transparent cell wall having an interior surface; (b) an electrolyte, disposed within the cell wall, and containing an iodide based species; (c) a transparent electrically conductive coating disposed on the interior surface; (d) an anode disposed on the conductive coating, the anode including: (i) a porous film containing titania, the porous film adapted to make intimate contact with the iodide based species, and (ii) a dye, absorbed on a surface of the porous film, the dye and the porous film adapted to convert photons to electrons; (e) a cathode disposed on an interior surface of the housing, and disposed substantially opposite the anode; (f) electrically-conductive metallic wires, disposed at least partially within the cell, the wires electrically contacting the anode and the electrically conductive coating, and (g) a second electrically conductive coating including an inorganic binder and an inorganic electrically conductive filler, the second coating bridging between and electrically communicating between each of the wires and the transparent coating, the wires adapted to boost collection of a current generated by the cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/658,661, filed Mar. 16, 2015, which is a continuation application ofU.S. patent application Ser. No. 14/082,460 filed Nov. 18, 2013, whichis a continuation application of U.S. patent application Ser. No.12/814,523, filed Jun. 14, 2010, which is a continuation-in-part (CIP)application of U.S. patent application Ser. No. 10/754,584, filed Jan.12, 2004, which draws priority from Israel Patent Application Serial No.153,895, filed Jan. 12, 2003; U.S. patent application Ser. No.12/814,523 is also a continuation-in-part (CIP) application of U.S.patent application Ser. No. 12/618,741, filed Nov. 15, 2009, which drawspriority from PCT Application No. IL2008/000671, filed May 15, 2008,which draws priority from U.S. Provisional Patent Application Ser. No.60/917,941, filed May 15, 2007; and a continuation-in-part (CIP)application of U.S. patent application Ser. No. 12/744,914, filed May26, 2010, which draws priority from PCT Application No. IL2008/001550,filed Nov. 26, 2008, which draws priority from U.S. Provisional PatentApplication Ser. No. 60/990,307, filed Nov. 27, 2007, all of which arehereby incorporated by reference for all purposes as if fully set forthherein.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to photovoltaic cells (also known as solarcells) for producing electricity from sunlight, and for improved systemsand methods therefor.

The invention has particular relevance for solar cells of the dyesensitized type, and is applicable to other types of solar cells, anddevices such as screen displays and electronic or defrostable windowswhere a high current density of operation at minimal ohmic loss isadvantageous. A further application is in solar thermal systems (e.g.,solar water heaters) where heat and power may be provided from the samecollector area/structure.

Dye-sensitized photovoltaic cells for producing electricity fromsunlight have been disclosed by U.S. Pat. No. 5,350,644 to Graetzel, etal. U.S. Pat. No. 5,350,644 teaches a photovoltaic cell having alight-transmitting, electrically-conductive layer deposited on a glassplate or a transparent polymer sheet to which a series of titaniumdioxide layers have been applied, in which at least the last titaniumdioxide layer is doped with a metal ion that is selected from a divalentor trivalent metal.

Following U.S. Pat. No. 5,350,644, U.S. Pat. No. 6,069,313 to Kayteaches a plurality of series-connected cell elements arranged asseparate parallel elongated stripes on a common electrically insulatingtransparent substrate. Each element includes a light facing anode, acounter-electrode or cathode, and an intermediate, light-sensitiveelectrically-insulating porous layer separating the anode from thecathode. The pores of the intermediate layer are at least partiallyfilled with a liquid phase, ion-transferring electrolyte and a lightsensitive dye. An additional current collecting layer of a transparent,electrically-conducting material is situated between the substrate(glass or transparent polymer) and each of the anode and cathode. Theanode and cathode of a given cell provide a direct-current voltage whenthe anode is exposed to light and series assemblies of cells may readilybe built up. The cathode of each succeeding element is connected withthe intermediate conducting layer of the preceding anode element, over agap separating the respective intermediate layers of these two elements.

The cells of the above-cited prior art (an example of which is providedin FIG. 1a ) are much closer conceptually to battery cells than toconventional photovoltaic cells, since the charge generators areseparated by an electrolyte and are not in direct contact. These cellshave two electrodes separated by an electrolyte, with one electrode (thephotoelectrode) facing the sun. Each electrode is supported on its owncurrent collector, usually a sheet of conducting glass, which is opticalglass coated on one side with a thin (about 0.5 microns) transparentlayer usually based on electrically-conductive tin oxide, and theconducting glass sheets act as transparent walls of the dye cell.

A transparent polymer may be used in place of glass to support the tinoxide. The photoelectrode includes a transparent porous layer about 10microns thick (in contact with the tin oxide layer) based on titania,having a nanocrystalline characteristic particle size of 10-50 nm,applied by baking onto the conductive glass or transparent polymer, andimpregnated with a special dye. The baked-on titania layer is applied indispersion form by doctor blading, rolling, spraying, painting, gravureprinting, screen printing or printing, but the baking step in someexperimental procedures is in excess of 400° C., requiring the use ofconducting glass rather than plastic for supporting the titania layer.Other processing procedures for the titania layer are feasible, such asreduced temperature baking, or pressing, usually with some sacrifice inefficiency.

The other electrode (the counter electrode) includes a thin layer ofcatalyst (usually containing a few micrograms of platinum per square cm)on its respective sheet of tin-oxide coated conductive glass ortransparent plastic. The electrolyte in the cell is usually an organicsolvent with a dissolved redox species. The electrolyte is typicallyacetonitrile or a higher molecular weight nitrile, with the redoxspecies being dissolved iodine and potassium iodide—essentiallypotassium tri-iodide. Other solvents and phases may be used, however.

U.S. Pat. No. 5,350,644 to Graetzel, et al. discloses various dye cellchemistries, especially different dyes based on ruthenium complexes.Photons falling on the photoelectrode excite the dye (creating activatedoxidized dye molecules), causing electrons to enter the conduction bandof the titania and to flow (via an outer circuit having a load) to thecounter-electrode. There, the electrons reduce tri-iodide to iodide inthe electrolyte, and the iodide is oxidized by the activated dye at thephotoanode back to tri-iodide, leaving behind a deactivated dye moleculeready for the next photon. U.S. Pat. No. 5,350,644 discloses that suchdye cells can attain a solar-to-electric conversion efficiency of 10%.

The cells disclosed by U.S. Pat. No. 5,350,644 to Graetzel, et al. (seeFIG. 1a), are based on two sheets of conductive glass sealed withorganic adhesive at the edges (the conductive glass projects beyond theadhesive on each side, allowing for current takeoff). These cellsoperate at a voltage of about 650 mV and a current density of 15mA/square cm under peak solar illumination, with the counter-electrodebeing the positive pole. It is asserted therein that since the materialsand preparation methods are low cost and the titania layer can beprepared in large areas, such cells could potentially provide a goodroute to low-cost photovoltaic cells. It is further argued that theremight be significant cost savings over classical single crystal orpolycrystalline silicon cells and even more recent thin-filmphotovoltaic cells, since these are all high cost and rely on expensiveand often environmentally problematic raw materials, together withcomplex, costly, semiconductor industry processing equipment andproduction techniques. These drawbacks include the use of vacuumdeposition and laser methods, clean-room protocols, use of toxichydrides such as silane, phosphine etc., as raw materials, and the useof toxic active-layer materials containing cadmium, selenium ortellurium.

The ohmic loss via the conductive glass coated with tin oxide is a majorproblem of such cells. The tin oxide coating is extremely thin, beinglimited in thickness usually to below one micron due to the need tomaintain a high light transmittance through to the dye/titania layer ofthe photoanode. Moreover, tin oxide is only semi-conductive and ismechanically weak, such that the current takeoff is significantlylimited by such a cell design.

A photovoltaic cell having electrically conducting coatings on spaced,glass support panes is disclosed by U.S. Pat. No. 6,462,266 to Kurth,which is incorporated by reference for all purposes as if fully setforth herein. As shown in FIG. 1b , a portion of a photovoltaic cell 1is shown in a cross-section with two mutually distanced support panes 2and 3, which in their border zones are held by a sealing system 4, whichextends along the whole circumference. The inner surfaces of supportpanes 2 and 3 are coated each with a conductive layer 5, and 6,respectively. Layers 5 and 6 are formed by a suitable metal or metaloxide, in the present case, SnO₂. On layers 5 and 6, an arrangement ofparallel conductor leads 7 and 8 are provided, preferentially made fromsilver or a silver alloy, or from copper or a copper alloy. Theseconductor leads are coated each with an insulating coating 10, whichinsulates conductor leads 7 and 8 electrically towards the interior ofthe cell. Coating 10 consists of a glass free of heavy metals, which wasapplied as a glass flow on conductor leads 7 and 8. Onto conductor leads7 and 8 insulated by the glass coating 10, a further electricallyconductive layer 11 and 12 respectively, made from tin oxide or asimilar material, can be applied in order to obtain a still higher yieldof photovoltaic cell 1. In the border zones of seals 13 and 14, noelectrically conductive layers 5 and 6 are provided, i.e., such layershave been eliminated from this zone using a sandblasting process. Inthis manner, possible short circuits via the seals 13 and/or 14 areavoided. Onto these two seals, a thin layer 15 of a low melt solderingtin is applied in such a manner that exterior weather influences alsocan not act onto photovoltaic cell 1.

The photovoltaic cell taught by U.S. Pat. No. 6,462,266 has reducedohmic loss with respect to the cell disclosed by U.S. Pat. No. 5,350,644to Graetzel, et al., because conductor leads 7 and 8 are good conductors(e.g., silver paste screen printed on and fired at 600° C.), and becausethe overall thickness of conducting materials has been increased. Itmust be emphasized that U.S. Pat. No. 6,462,266 teaches strips appliedonto tin oxide coated glass and does not teach, nor fairly suggest, theapplication of conductive strips directly onto the glass (e.g., prior tothe application of a tin oxide layer). Furthermore, the emphasis is onsingle cell construction with no advantage offered for construction of amulti-cell module. Most significantly, the periphery (i.e., the sides)of the cells is devoid of any current takeoff means, any current takeoffbeing made on the active sun-facing surface of the cell, resulting in awaste of available area. Consequently, the improvement in the cellperformance is far from sufficient. U.S. Pat. No. 6,462,266 alsoemphasizes the application of two separate layers of tin oxide, as wellas very high temperature processing that precludes plastic cells.

U.S. Patent Publication No. 20030108664 discloses a substrate withrecessed conductors prepared from silver compositions. However, no meansfor protecting the conductors from corrosion are taught. Moreimportantly, there is no specific means described for achieving therequisite current takeoff without wasting available area.

To date, there has been no real commercialization of photovoltaic dyecells, despite the great techno-economic potential thereof. Theprincipal problems remaining include scale-up of cells to widths muchabove one centimeter—and areas much above 50 square cm—due to excessiveohmic losses from the poorly conducting tin oxide layers on the glass orplastic, long term stability of the dye, and difficulties of sealing thecells against long-term dryout and performance degradation. A furtherproblem in prior art cells and modules has been excessive surface areawasted in seals and conducting paths on the sun-facing side of the cellor module. The active current-producing area in such cases is often lessthan 70% of the geometric area (footprint) of the cell or module,providing a poor effective efficiency from the available area.

There is therefore a recognized need for, and it would be highlyadvantageous to have, an electrochemical cell, powered by sunlight, thatis simple, efficient and robust, and successfully addresses the manifestshortcomings of the prior art.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided aphotovoltaic cell for converting a light source into electricity, thecell including: (a) a housing for the photovoltaic cell, the housingincluding an at least partially transparent cell wall, the cell wallhaving an interior surface; (b) an electrolyte, disposed within the cellwall, the electrolyte containing an iodide based species; (c) an atleast partially transparent electrically conductive coating disposed onthe interior surface, within the photovoltaic cell; (d) an anodedisposed on the at least partially transparent electrically conductivecoating, the anode including: (i) a porous film containing titania, theporous film adapted to make intimate contact with the iodide basedspecies, and (ii) a dye, absorbed on a surface of the porous film, thedye and the porous film adapted to convert photons to electrons; (e) acathode disposed on an interior surface of the housing, the cathodedisposed substantially opposite the anode; (f) a plurality ofelectrically-conductive metallic wires, disposed at least partiallywithin the photovoltaic cell, the metallic wires electrically contactingthe anode and the at least partially transparent electrically conductivecoating, and (g) a second electrically conductive coating including aninorganic binder and an inorganic electrically conductive filler, thesecond coating bridging between and electrically communicating betweeneach of the electrically-conductive metallic wires and the at leastpartially transparent electrically conductive coating, theelectrically-conductive metallic wires configured to boost collection ofa current generated by the cell.

According to another aspect of the present invention there is provided aphotovoltaic cell for converting a light source into electricity, thecell including: (a) a housing for the photovoltaic cell, the housingincluding an at least partially transparent cell wall, the cell wallhaving an interior surface; (b) an electrolyte, disposed within the cellwall, the electrolyte containing an iodide based species; (c) an atleast partially transparent electrically conductive coating disposed onthe interior surface, within the photovoltaic cell, the at leastpartially transparent electrically conductive coating including tinoxide; (d) an anode disposed on the at least partially transparentelectrically conductive coating, the anode including: (i) a porous filmcontaining titania, baked on to the electrically conductive coating, theporous film adapted to make intimate contact with the iodide basedspecies, and (ii) a dye, absorbed on a surface of the porous film, thedye and the porous film adapted to convert photons to electrons; (e) acathode disposed on an interior surface of the housing, the cathodedisposed substantially opposite the anode; (f) a plurality ofelectrically-conductive metallic wires, disposed at least partiallywithin the photovoltaic cell, the metallic wires electrically contactingthe anode and the at least partially transparent electrically conductivecoating, and (g) a second electrically conductive coating including abinder and an electrically conductive filler, the second coatingbridging between and electrically communicating between each of theelectrically-conductive metallic wires and the at least partiallytransparent electrically conductive coating, the second coating baked onto the electrically conductive coating, the electrically-conductivemetallic wires configured to boost collection of a current generated bythe cell.

According to yet another aspect of the present invention there isprovided a photovoltaic cell for converting a light source intoelectricity, the cell including: (a) a housing for the photovoltaiccell, the housing including an at least partially transparent cell wall,the cell wall having an interior surface; (b) an electrolyte, disposedwithin the cell wall; (c) an at least partially transparent electricallyconductive coating disposed on the interior surface, within thephotovoltaic cell; (d) an anode disposed on the at least partiallytransparent electrically conductive coating, the anode including: (i) aporous film, baked on to the electrically conductive coating, the porousfilm adapted to make intimate contact with the electrolyte, and (ii) adye, absorbed on a surface of the porous film, the dye and the porousfilm adapted to convert photons to electrons; (e) a cathode disposed onan interior surface of the housing, the cathode disposed substantiallyopposite the anode; (f) a plurality of electrically-conductive metallicwires, disposed at least partially within the photovoltaic cell, themetallic wires electrically contacting the anode and the at leastpartially transparent electrically conductive coating, and (g) a secondelectrically conductive coating including a binder and an electricallyconductive filler, the second coating bridging between and electricallycommunicating between each of the electrically-conductive metallic wiresand the at least partially transparent electrically conductive coating,the second coating baked on to the electrically conductive coating.

According to further features in the described preferred embodiments,the inorganic, electrically conductive filler is selected from the groupconsisting of metal powders, metal oxides, metal carbides, metalborides, metal silicides, and metal nitrides.

According to still further features in the described preferredembodiments, the inorganic, electrically-conductive filler includestitanium nitride.

According to still further features in the described preferredembodiments, the photovoltaic cell further includes: a currentcollection element, disposed at least partially on a side of the cellwall, the current collection element electrically connected to themetallic wires, and configured to remove therethrough the currentproduced by the cell.

According to still further features in the described preferredembodiments, the second coating contains an electrically-conductivemetal material selected from the group of titanium, tungsten,molybdenum, chromium, vanadium and tantalum.

According to still further features in the described preferredembodiments, the transparent conductive coating includes a tin-oxidebased conductive coating.

According to still further features in the described preferredembodiments, the conductive filler contains an inorganicelectrically-conducting material in a form selected from the groupconsisting of powders, fibers, flakes, and whiskers.

According to still further features in the described preferredembodiments, the second coating contains an electrically-conductingmaterial selected from the group consisting of tin oxide, magnelioxides, spinel oxides, and perovskite oxides.

According to still further features in the described preferredembodiments, the binder contains at least one inorganic binder materialselected from the group consisting of alumina and silica.

According to still further features in the described preferredembodiments, the binder contains at least one inorganic binder materialincluding a glass.

According to still further features in the described preferredembodiments, disposed in the interior surface of the cell wall is aplurality of grooves, each of the grooves at least partially containingthe second coating and a wire of the wires.

According to still further features in the described preferredembodiments, the porous film containing titania is baked on to theelectrically conductive coating.

According to still further features in the described preferredembodiments, the second coating is baked on to the electricallyconductive coating.

According to still further features in the described preferredembodiments, the electrically-conductive metallic wires are based on atleast one metal selected from the group of metals consisting oftitanium, tungsten, molybdenum, chromium, and tantalum.

According to still further features in the described preferredembodiments, the second coating contains an electrically-conductivematerial selected from the group consisting of metal powders, metaloxides, metal carbides, metal borides, metal silicides, and metalnitrides.

According to still further features in the described preferredembodiments, disposed in the interior surface of the cell wall is aplurality of grooves, each of the grooves at least partially containingthe second coating and a wire of the wires.

According to still further features in the described preferredembodiments, the iodide based species includes tri-iodide or iodine.

According to still further features in the described preferredembodiments, the housing of the photovoltaic cell includes an openingfor replacement of at least one component of the cell.

According to still further features in the described preferredembodiments, this component is the electrolyte.

According to still further features in the described preferredembodiments, this component is a dye.

According to still further features in the described preferredembodiments, two or more of the photovoltaic cells are electricallyconnected in series.

According to still further features in the described preferredembodiments, the photovoltaic cells are electrically connected in seriessolely by the current collection element.

According to still further features in the described preferredembodiments, the interior surface has at least one groove, and withinthe at least one groove is disposed the electrically conductive elementfor conducting a current produced by the photovoltaic cell.

According to still further features in the described preferredembodiments, the conductive material is physically isolated from theelectrolyte by a material that is chemically inert to the electrolyte.

According to still further features in the described preferredembodiments, the conductive material is physically isolated from theelectrolyte by a second material, the second material being chemicallyinert to the electrolyte.

According to still further features in the described preferredembodiments, the second material is a substantially non-conductivematerial.

According to still further features in the described preferredembodiments, the second material is a second conductive material.

According to still further features in the described preferredembodiments, the second conductive material includes a material selectedfrom the group consisting of graphite, tin oxide, and titanium nitride.

According to still further features in the described preferredembodiments, the conductive material is electrically associated with alayer of tin oxide. According to still further features in the describedpreferred embodiments, the at least partially transparent conductivecoating includes tin oxide. According to still further features in thedescribed preferred embodiments, the electrical resistance of thecoating exceeds 10 ohms per square. According to still further featuresin the described preferred embodiments, the electrical resistance of thecoating exceeds 20 ohms per square.

According to still further features in the described preferredembodiments, the at least partially transparent conductive coatingincludes tin oxide, and the electrical resistance of the coating exceeds30 ohms per square. Preferably, a low-cost, low-grade tin oxide coatingcan be used, having an electrical resistance exceeding 50 ohms persquare, and even exceeding 50 ohms per square.

According to still further features in the described preferredembodiments, the tin oxide is a low-grade tin oxide prepared by aprocess selected from the group consisting of sol-gel process, vapordeposition process, plasma, and dip spray process.

According to still further features in the described preferredembodiments, the photovoltaic cell further includes a seal selected fromthe group consisting of gasket and O-ring, and a closure for pressuringthe seal so as to seal the photovoltaic cell, the closure selected fromthe group consisting of crimp closure and bolted closure.

According to still further features in the described preferredembodiments, the cell wall includes plastic, or is made entirely ofplastic.

According to still further features in the described preferredembodiments, an edge seal of the cell wall is made primarily of amaterial selected from the group consisting of low-temperature glass,polymer, inorganic adhesive, and

According to still further features in the described preferredembodiments, the conductive coating includes titanium nitride and abinder that is substantially chemically inert with respect to theelectrolyte.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

In the drawings:

FIG. 1a is a cross-section of a photovoltaic cell taught by U.S. Pat.No. 5,350,644 to Graetzel et al.;

FIG. 1b is a cross-section of a photovoltaic cell as disclosed by U.S.Pat. No. 6,462,266 to Kurth;

FIG. 2 is a schematic perspective illustration of a grooved cell wall,according to one aspect of the present invention;

FIG. 3a is a schematic side, cut-away view of a preferred embodiment ofthe inventive photovoltaic cell;

FIG. 3b is a schematic, cross-sectional view of a groove partiallyfilled with a first conductive material, which is encapsulated andsealed by a second conductive material;

FIG. 4 is a schematic, cut-away side view of a two-cell module, shownwithout side-placed contacts.

FIG. 5a is a schematic perspective view of a conductive cell wall havingstrips deposited directly onto the surface;

FIG. 5b shows a cell having grooves for filling with a conductingmaterial, the grooves passing through holes in a top surface of the cellfor facile current take-off;

FIG. 6a is a schematic, perspective illustration of a modular cell ofthe present invention, having an encapsulated, conducting perimeterstrip for interconnecting with additional modular cells;

FIG. 6b is a schematic, cross-sectional view of a modular cell of thepresent invention, having a single, sealed cell wall encompassing theelectrical components of the cell;

FIG. 7 is a schematic, cross-sectional view of cell of the presentinvention having a crimp and gasket sealing system;

FIG. 8 is a schematic perspective view of a sheet plastic honeycombsupport structure for housing photovoltaic cells, according to thepresent invention;

FIGS. 9a and 9b are schematic, cross-sectional views of fixed flat plateconventional solar water heaters or tracking trough-type collectors forsolar thermal power installations integrated with cells or panels of thepresent invention, for simultaneous production of electricity and hotwater using the basic supporting structural unit and collector area ofthe solar water heaters/collectors, and

FIGS. 10a-10c are schematic diagrams showing the construction of a dyecell containing an electrically-conducting element made of a conductivemesh.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles and operation of the photovoltaic cells according to thepresent invention may be better understood with reference to thedrawings and the accompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

The present invention overcomes these and other problems and paves theway to the manufacture of an efficient, commercially viable device.Various aspects and embodiments of the present invention are describedhereinbelow:

One aspect of the present invention provides a means for greatlyreducing the effective ohmic loss from the electrically-conductingsupport of the titania-based photoactive layer of photovoltaic dyecells. This support is usually poorly-conducting, tin oxide coated glassor plastic alone, and usually necessitates a width under 1 cm, in whichthe seal (usually a polymer strip of 1-2 mm width) can take up anexcessive proportion. The present invention enables the construction oflarge area (50-200 square cm), wide (2-5 cm or more) dye cells.Moreover, the fraction of cell or module footprint taken up byconductors and seals on the sun-facing surface of cells is reducible toan acceptable level of less than 10%.

One major approach of the present invention is the incorporation ofconductivity-augmenting strips (at periodic intervals on the surface ina striped or meshed pattern) on top of or beneath the face of the glassor plastic, while the strips are in electrical contact with a tin oxidebased or other electrically-conductive transparent layer covering theglass or plastic and on top of or beneath these strips. The strips aredesigned to shade only a small fraction (preferably less than 5%) of theavailable light entering the cell, and can be applied directly on theglass or plastic. The strip dimensions (length, width, thickness andnumber of strips) and the conductivity of the strip material must beconsistent with the conductivity-boosting properties required from thephotoelectrode. Although it might be possible to use for the stripssimply applied and unprotected common conductors such as silver, copper,aluminum, nickel and the like, the corrosive nature of the electrolyte(especially the presence of iodine and nitrites in the liquid phase)usually obligates use of more corrosion-resistant metals or conductivematerials (such as titanium, metal carbides etc.), or at the very least,sealed-in strips of the common conductors.

In one preferred embodiment, the strips are deposited directly onto thesurface of a glass or a plastic coated with a transparent conductiveoxide such as tin oxide. The strips are based on molybdenum, chromium,tantalum, vanadium and/or titanium, in the form of metal, alloy, metaloxides, carbides, nitrides borides or silicides. Preferably, a vaporphase deposition process is used such as sputtering, in conjunction withmechanical or chemical masking, to achieve the strip pattern. In thecase of chromium, electro-deposition of strips is also possible. Sincethe external surfaces of strips may still be active to catalyze at thephotoanode unwanted, efficiency-reducing recombination of chargecarriers, an inert-to-recombination tin oxide (or other inert,conducting covering layer such as titanium nitride) can advantageouslybe applied to these external surfaces. Also, the ends of the strips canterminate in a perimeter strip around the edge of the glass, and/orcontinue over onto the edge of the glass, for cell sealing or currenttakeoff purposes.

In another preferred embodiment, the strips are inert foils or wires(e.g., titanium, molybdenum, or clad materials such as titanium that isclad on copper) bonded directly onto the tin oxide coated glass using aninert conducting adhesive. The adhesive can include an inert, conductingfiller (e.g., titanium powder, molybdenum powder, tungsten powder,graphite powder or titanium nitride powder) combined with an inertbinder from the phosphate, silicate, low temperature glasses, aluminate,titanate or zirconate families (e.g., potassium silicate), such thatboth the filler and the binder are stable during the high-temperatureprocessing of the titania photoactive layer and during exposure to theelectrolyte within the cell. If the titania is processable at lowertemperatures (e.g., up to 300° C.), then inert polymer binders such asTeflon® may be used. In the case of the conductors continuing over ontothe edge of the glass, an important benefit is that current may beremoved from cells without seriously reducing the available area of thecell.

In another preferred embodiment, the strips are located in grooves inthe glass or plastic surface, below, but in electrical contact with, thetin oxide layer. In this embodiment, the glass or plastic is firstgrooved, and a conductive transparent layer of tin oxide is applied byvacuum deposition, spray pyrolysis or sol-gel means (depending on theglass or plastic used) such that tin oxide enters also at least partlyinto the grooves to ensure maintenance of surface electrical continuitywith the groove contents. After this step, at least one of electricallyconductive strips, wires or conducting paste is introduced into thegrooves, and an additional, optionally electrically conductive layerbonds, seals and encapsulates the strip, wire or paste in the grooves,preferably filling each groove up to the surface of the glass orplastic. In the case of cell walls based on plastic, the groovestructure may be pre-molded into the plastic. In the case of glass,stresses in the grooved glass can be reduced by annealing in conjunctionwith mechanical grooving. Alternatively, the grooving may be performedusing laser, abrasive, ultrasonic or chemical etching means.

The above procedure describes coating the grooved glass or plastic witha conductive tin oxide layer before filling the grooves with conductor,but it is also feasible to coat with tin oxide following groove filling.Due to the corrosive nature of the electrolyte, useful materials for thestrips, wires, and pastes are based on titanium, tungsten, molybdenum,chromium, tantalum, graphite, or carbon, or clad materials such astitanium clad on copper and if well sealed-in, also silver, copper,aluminum, nickel, and tin. The optionally conductive paste orencapsulant may also advantageously be made from inert conductingpowders, fibers, flakes, or whiskers such as graphite, carbon black, tinoxide, magneli oxides, spinel or perovskite oxides, or tungsten,tantalum, titanium, vanadium, chromium or molybdenum as metal powders,oxides, carbides, borides, silicides, or nitrides, together with anorganic or inorganic curable binder. Useful inorganic bindercompositions include silicates, aluminates, phosphates, zirconates andlow melting glasses that may include silica. If the sealing layer ispreferred to be non-conductive, then the conductive filler is simplyomitted. The conductor beneath the sealing encapsulant layer may, ifnecessary, be provided by paste, electrochemical plating, plasma orvapor deposition means.

Onto the tin oxide coated glass or plastic with the surface orsubsurface strips, the titanium oxide layer is deposited as in aconventional dye cell (e.g., by baking or pressing), and afterimpregnation with dye, acts as the photoanode. Current takeoff is fromthe extremities of the strips or grooves, using a separate paste layeror contacting metal contacts.

A similar ohmic loss reducing strategy may be used for thecounter-electrode, based on a glass or plastic wall which can be coated(like the anode) with a transparent, conducting tin oxide layer, and canalso be fitted with overlaying strips, or grooves containing conductiveelements. As is usual for conventional dye cell counter-electrodes, thetin oxide surface is coated with a thin coating of platinum catalyst.The platinum may be in supported form (e.g., supported on carbon orgraphite) or may be substituted by a non-noble electrocatalystequivalent, such as a metal carbide or a tungsten bronze oxide, alone orsupported on carbon or graphite. For example, the platinum layer may bedeposited on the tin oxide coated glass or plastic by thermaldecomposition of a platinum precursor (e.g., chloroplatinic acidsolution), by electrochemical plating, or by vapor deposition means suchas sputtering. Alternatively, a layer of catalyst in continuous form(e.g., by spray means) or web form (e.g., by printing means), supportedif necessary by an inert polymer binder such as Teflon®, may be appliedto a grooved glass or plastic wall fitted with conductive strips andoptionally coated with tin oxide. Current takeoff from each electrode isby a current collecting contact (strip or wire or paste) that connectsoutside the cell with the strips or wires or paste emerging on top ofthe glass/plastic or from the grooves in the glass/plastic. Inter-cellconnection may be effected by joining of these current collectors(mechanical means, soldering or welding means, etc.). It is particularlyeasy to connect up large numbers of cells in series to make a solarpanel.

In another aspect of the present invention, appropriate especially forcases where the titania layer must be baked at high temperatures (e.g.,450° C.) significantly above the tolerance range of plastics, it ispossible to dispense entirely with the need for a tin oxide coating oncell glass or plastic walls. The titanium oxide layer is prepared on aseparate heat-resistant underlying support at 450° C. by baking on.

The underlying support is preferably an open, inert,electrically-functional structure, e.g., a conducting porous mat (suchas carbon fiber veil, or titanium metal mesh). Such support materialsare, if necessary, made inert to the iodine redox reaction by coatingwith an inert material having poor or negligible electro-catalyticproperties for the iodine redox reaction (such as tin oxide or titaniumnitride).

Once the titania has been baked on, an additional porous inertconductive underlayer (i.e., between the titania and thecounter-electrode) or overlayer (i.e., between the titania and the uppercell wall facing the sun) such as tin oxide, titanium nitride or magnelioxide can be added. Such an underlayer or overlayer can be depositedonto the titania using spray or plasma means. Alternatively, theconductive layer can be bonded (if necessary) using a suitable inertpolymer binder (such as Teflon®) that is sinterable at 300° C. or less.The conductive layer can be added on top of or under the layer oftitania. It should be mentioned that the titania with a tin oxideoverlayer gives a translucent electrode.

Such support structures (e.g., via a suitable tab on one or both ends ofthe mesh) can sealably be brought through polymer seals or gaskets toserve as current collectors between adjacent cells. Thecounter-electrode can be made similarly using a carbon fiber veil ortitanium mesh. Here, of course, there is no need for a baked titanialayer or titanium nitride inert coating, but instead, the mesh or veilcan be lightly catalyzed with platinum, or preferably coated with aporous catalytic layer of graphite or carbon (optionally catalyzed)bonded using a suitable inert binder such as Teflon®.

Of course, the use of two conducting meshes or veils in a cell willoblige the use of a separator in the cell. Although porous plasticseparators are possible, greatest endurance is expected using inertglass fiber porous separators.

In another preferred embodiment of the present invention, a surface 40of an at least semi-transparent cell wall 50 is provided with aplurality of grooves 60, as illustrated schematically in FIG. 2. Surface40 is an interior surface of the cell, as will be evident from FIG. 3aand from the description hereinbelow. Cell wall 50 is typically made ofglass or plastic. Grooves 60, which can be of various shapes anddesigns, typically have a depth of tens to hundreds of microns(micrometers).

FIG. 3a provides a schematic side, cut-away view of a photovoltaic cell100 of the present invention having an anode cell wall 50 a and acathode cell wall 50 b, both provided with a plurality of grooves 60 ininterior surface 40. Grooves 60 are at least partially filled with aconductive material 80, which is typically in the form of electricallyconductive strips, wires or conducting paste.

Optionally and preferably, and as shown in FIG. 3b , an additionalelectrically conductive layer 82 bonds, seals and encapsulatesconductive material 80, filling each groove 60 up to interior surface 40of cell wall 50 a or 50 b. (If, via shrinkage on curing, the conductivefilling sinks appreciably below interior surface 40, as in the case of aconductive paste after curing, at least one additional application ofpaste may be required, or alternatively, the conductive paste may beapplied on top of a heat-removable, mechanically removable orchemically-removable spacing layer of paper, plastic, metal or othersuitable coating on the glass/plastic that has been cut to expose thegrooves).

Referring back to FIG. 3a , covering interior surface 40 of anode cellwall 50 a is an electrically-conductive transparent layer 42 a.Similarly, interior surface 40 of cathode cell wall 50 b is covered byan electrically-conductive transparent layer 42 b, which typicallyincludes a catalyst coating. Adjacent and substantially parallel toelectrically-conductive transparent layer 42 a is a titania/dye layer44. Between titania/dye layer 44 and electrically-conductive transparentlayer 42 b is disposed an electrolyte 46 that is absorbed in thetitania/dye layer.

The operation of photovoltaic cell 100 is similar to the cell disclosedin U.S. Pat. No. 5,350,644 to Graetzel, et al., and is well understoodby those skilled in the art.

The sealing of photovoltaic cell 100 can be performed in various ways.In FIG. 3a , photovoltaic cell 100 is sealed by an adhesive sealantlayer 48 disposed at the sides of cell 100.

Optionally and preferably, a fill tube 52 is disposed within adhesivesealant layer 48, to allow for periodic refilling/replacement ofelectrolyte 46 or the dye layer in titania/dye layer 44, as needed.

When cell wall 50 a or 50 b is based on plastic or similar materials,the groove structure may be cut or molded into the plastic. When cellwall 50 a or 50 b is based on glass or the like, annealing may beperformed in conjunction with mechanical grooving, so as to reducestresses in the grooved cell wall. Alternatively, it is possible tocarry out the grooving using laser, abrasive, air jet, water jet,ultrasonic, chemical etching, or other means known in the art. Grooves60 are rectilinear, V-shaped or U-shaped or of another toolable ormoldable profile. Preferably, there should not be a sharp angle at theouter extremity of grooves in order to better accept and support acontinuous coating. For example, the outer edge of the groove may begiven a radius as part of the grooving operation or as a separate step.Following curing of the paste or encapsulating layer, the glass orplastic is coated with tin oxide by conventional spray, vapordeposition, plasma deposition, or sol-gel means.

It has been found that although prior art cells demand only highestquality grade tin oxide coatings with highest conductivities (usuallybelow 10 ohms per square) and correspondingly high cost, the presentinvention utilizes grooves or strips so as to allow the use of muchlower grade tin oxides, even in the relatively poor conductivity rangeof 20-100 ohms/square and above. This allows for the utilization of lessexpensive materials and manufacturing techniques. It is also possible tocoat the grooved glass or plastic with tin oxide (prior to the bondingof the strips or wires or paste in the grooves by means of theconducting adhesive or sealant) and conductivity continuity is assuredby at least part of the tin oxide entering into the grooves and therebycontacting the conducting filling.

Similarly, in another preferred embodiment, it is possible to cut thegrooves in standard, commercially-available tin oxide coated glass orplastic and then apply (e.g., by coating, printing or spraying,advantageously with the help of a mask) and creating over the grooves athin bridging layer of electrically conducting paste (i.e., bridgingonto the tin oxide) to ensure electrical continuity.

Although Graetzel-cell technology has been traditionally been limited tocell walls of specialized glass that is suitable for the hightemperature preparation/bonding of the titania layers, recently, goodquality titania layers have been prepared without recourse to suchelevated temperatures by, inter alia, mechanical pressing of titanialayers (suspended in a solvent, and applied by brushing, spraying orrolling methods) after evaporating off the solvent (see U.S. PatentApplication No. 20020106447 to Lindstrom, et al., which is incorporatedby reference for all purposes as if fully set forth herein). It must beemphasized that the present invention is especially suited to dye cellswith pressed layers and excellent performance is obtained, especially ifthe titania layer is deposited by electrophoresis prior to pressing.

FIG. 4 is a cut-away side view of a two-cell module, shown withoutside-placed contacts. Each groove 60 is partially filled with conductingmaterial 80, and then with an insulating material 84. Preferably,insulating material 84 is a sealant, such that the sealant canadvantageously serve also as a sealing barrier between adjacent cells100, 200. Heat-sealable materials (e.g., Suryln®), or curable materials(e.g., epoxy, polytetrafluoroethylene, inorganic adhesives such asceramic adhesives, and low temperature glass sealants fireable up to thetitania baking temperature) are suitable for this purpose.

It must be emphasized that cells 100, 200 must be electrically isolatedfrom one another. To this end, it is necessary to have a break 86 inboth tin oxide layer 72 a on the anode side and tin oxide layer 72 b onthe cathode side. In another preferred embodiment, strips 90 aredeposited directly onto the interior surface 140 of a conductive glassor plastic cell wall 150, as shown in FIG. 5a . The strips are based onmolybdenum, chromium, tantalum, vanadium, and/or titanium in the form ofmetal, alloy, or metal oxides, carbides, nitrides, borides or silicides,in which a vapor phase deposition process may be used such assputtering, in conjunction with mechanical or chemical masking toachieve the strip pattern. (In the case of chromium, electro-depositionof strips is also possible, while titanium may be applied as a metalstrip or clad strip such as titanium on copper onto a conductingadhesive). Since the external surfaces of strips 90 may still besensitive to corrosion or active to parasitic catalysis, at thephotoanode, of unwanted (efficiency-reducing) recombination of chargecarriers, an inert conductor such as titanium nitride) canadvantageously be applied to these external surfaces and can also act toencapsulate against corrosion. For example, strips could be first laiddown on plain glass or plastic and then covered with tin oxide. In thisapproach, the strip thickness is preferably less than the wet appliedtitania layer thickness before baking. It must be emphasized that,unlike the prior art of U.S. Pat. No. 6,462,266 to Kurth, the ends ofthe conductive strips preferably terminate in a perimeter strip aroundthe edge of the glass/plastic, as shown in FIG. 7, and/or continue overonto the edge of the cell wall, for cell sealing or current takeoffpurposes. The latter strategy allows for a high utilization of celltotal area (about 90%), since current takeoff is performed mainly at theedges of the cell, and not in the plane of illumination.

Due to the corrosive nature of the electrolyte, we have found usefulmaterials for the strips, wires, and pastes to be based on titanium,tungsten, molybdenum, chromium, tantalum, bismuth, graphite, or carbon,and if well sealed in, also silver, copper, aluminum, nickel, tin andsolder, while the paste or encapsulant may also advantageously be frominert conducting powders, fibers or whiskers such as graphite, carbonblack, tin oxide, magneli oxides, spinel or perovskite oxides, ortungsten, tantalum, titanium, vanadium, chromium or molybdenum as metalpowders, oxides, carbides, borides, suicides, or nitrides, together withan organic or inorganic curable binder. The conductor beneath thesealing encapsulant layer may if necessary be provided by paste,electrochemical plating, plasma, chemical deposition, metalizing, screenprinting, sputtering or vapor deposition means. In contrast to U.S. Pat.No. 6,462,266, the conductor may be laid down at convenient lowertemperatures (e.g., up to 200° C.) enabling application onto plastics.As described above, the sealant in the grooves (or covering the coatedstrips) may alternatively be non-conductive, based on inert material,and the sealant layer can advantageously serve as a dividing barrierbetween adjacent cells.

Onto the tin oxide coated glass or plastic with the surface orsubsurface strips, the titanium dioxide layer is deposited as in aregular dye cell (e.g., by baking or pressing), and after impregnationwith dye and electrolyte, acts as the photoanode. Current takeoff isfrom the extremities of the strips or grooves, outside the cell itself,using a separate paste layer or contacting metal contacts. Theextremities are advantageously sealed off using polymer or glasssealants.

A similar ohmic loss reducing strategy may be used for the counterelectrode, based on a glass or plastic wall fitted with overlayingstrips, or grooves containing conductive elements, optionally coatedwith tin oxide, with (as is usual for dye cell counter-electrodes) athin catalyst coating (such as platinum, or a non-noble electro-catalystequivalent such as a metal carbide or oxide, alone or supported oncarbon or graphite). For some applications, high surface area carbonsand graphites provide adequate catalytic effectivity. For example, aplatinum layer may be deposited on the glass, plastic (or tin oxidecoated versions of these) by electrochemical plating or vapor depositionmeans such as sputtering. Alternatively, a layer of catalyst incontinuous (e.g., by spray means) or web form (e.g., by printing means),supported if necessary by a binder such as polytetrafluoroethylene(Teflon®), may be applied to a glass or plastic wall fitted withconductive strips and optionally coated with tin oxide. In cells,current takeoff from each electrode is by a current collecting contact(strip or wire or paste) that connects outside the cell with the strips,wires or paste emerging on top of the glass/plastic or from the groovesin the glass/plastic. One particularly advantageous embodiment (e.g., inthe case of moldable plastic walls) is provided in FIG. 5b . Grooves 60,filled with a conducting material, pass through holes in top surface140, so as to enable current take-off from top surface 140, whileleaving the plate extremities free for sealing. Current takeoff ispreferably achieved by means of a collecting strip 66 connecting grooves60.

Inter-cell connection may be by joining of these current collectors(mechanical means, soldering or welding means, etc.). It is particularlyeasy to connect up large numbers of cells in series to provide a solarpanel.

FIG. 6a is a schematic, perspective illustration of a modular cell 250of the present invention, having an encapsulated, conducting perimeterstrip 260 for interconnecting with additional modular cells.

FIG. 6b is a schematic, cross-sectional view of a modular cell 275 ofthe present invention, having a single, sealed cell wall 50 encompassingthe electrical components of cell 275. Sealed cell wall 50 is preferablymade of plastic.

It should be emphasized that the present invention is applicable to allvarieties of cell electrolytes, including liquid phase, gel, molten saltand solid phase types including ion exchange membranes.

In yet another aspect of the present invention, we assemble and sealcells either using an inert sealant (e.g., Surlyn®,polytetrafluoroethylene, epoxy, or inorganic adhesive, or lowtemperature glass paste fireable at a temperature not exceeding thetitania process temperature), or via battery technology using strips,gaskets or O-rings and the like (crimping-bolting or pressing-closedcell and module edges). In a preferred embodiment, a mechanism forproviding periodic dye/electrolyte maintenance is included. In onepreferred embodiment, the cell sealing wall is permanently fitted withat least one resealable fill tube or tap for maintenance purposes. Insharp contrast to dye cells and modules of the prior art, which areirreversibly sealed, the cells of the present invention can bemaintained against dryout. This also enables cells and modules of thepresent invention to be assembled on a fast, automatic line that is moretypical of a battery facility than a complex, cost and labor-intensivesemiconductor plant.

Moreover, the above strategy for maintainable cell assembly, which,unlike irreversibly sealed cell assemblies, is maintainable with timeand is designed to be periodically (e.g., every several years)accessible (enabling opening/resealing in field or in plant), withfacility for dye/electrolyte top-up/replacement, as needed, can yieldvery long effective lifetimes of up to 25 years, rivaling the classicalsilicon solar cells. It must be emphasized that the dye cells of theprior art are notoriously prone to dryout and some designs becomeinoperative in only a few years, in full sunlight. The design andconfiguration of the cell of the present invention allow for adye/electrolyte renewal process based mainly on simple liquid transfertype chemical operations such as removal/washout of residual celldye/electrolyte, cell drying, and refilling with fresh dye/electrolyte.The replacement of other cell components in the battery type embodiment(e.g., with gasket or O-ring) is also possible under some designs (notethat the titania and other components are very stable with time). Amodule gasket is a molded, pressed, or extruded component definingadjacently positioned, hydraulically independent and sealed (butelectrically series-connectable) cell assemblies.

For slim cells (low weight, close spaced cell walls, minimum electrolyteand inter-electrode separation), positioning of gaskets in grooves atcell peripheries is an option.

Individual cells according to the present invention are the size ofconventional photovoltaic cells (e.g. 100-200 square cm or more) with athin, long rectangular strip form preferred for reduced ohmic drop. Forexample, an active cell area of 140 sq. cm (for example, 56 cm long by2.5 cm wide) would provide about 2.1 Amps at peak solar illumination at10% conversion efficiency. Only about 10% of the area is taken up bystrips (5%) and seals (5%), and the current takeoff from cell edges doesnot take up precious area on the cell surface. Consequently, thegeometric cell area is 155 square cm. A large module of 1 square meteractive area could be built, by way of example, with 65 of these cells inseries, providing at peak, 39V and 82 watts and attaining a reasonableconversion efficiency (about 8%) on the basis of the actual panel area.The cell/module edges may be sealed closed using sealants, or arepressed closed onto gaskets or O-rings by reinforcing edgings (e.g.metals such as copper, aluminum) held in place by crimping, bolts, clipsor other suitable means, and each cell can carry fill tubes or taps. Thecells/module thus are easily accessible for maintenance, and, whenequipped with a gasket or O-ring, enable all the cells to besimultaneously exposed for dye/electrolyte renewal when the module cover(glass or plastic) is removed. Cells need not necessarily be opened fordye/electrolyte renewal, but could be accessed via the fill tubes (as inFIG. 3a ). Although the design allows for direct injection ofdye/electrolyte through the seal material via a syringe needle, e.g.,via an elastomeric seal such as a gasket (FIG. 7), this does not assuregood resealing. Mechanical support across the module face, if needed,can be provided by bolts passing through the gasket in the interior areaof the module, or from support struts, etc., traversing the face of themodule.

By way of example, FIG. 7 shows a gasket 162 for sealing a photovoltaiccell 300, and a crimp closure 164 at each end of photovoltaic cell 300,for pressuring gasket 162 so as to effect the sealing. Current takeofffrom photovoltaic cell 300 is achieved using perimeter current takeoffstrips 166 a, 166 b.

Since some aspects of the present invention allow the construction ofplastic cells, we can, in addition to glass-walled cells, buildsealed-for-life, flexible, low cost plastic cells, using molded orextruded components and plastic sealing technology (heat, vibration orultrasonic welding). Such cells would be non-maintained and have acharacteristically-reduced lifetime (7-10 years) relative tomaintainable glass cells of the present invention. Longer-life,maintainable plastic cells could be fitted with a resealable fill tubeor tap for dye/electrolyte replacement, or have means allowing for sealbreakage, maintenance and resealing. Of course, plastic cells can alsobe built like glass cells with gasketing, as described hereinabove,allowing periodic opening/resealing for maintenance. One embodiment foreither approach, shown schematically in FIG. 8, is to insert individualcells into a sheet plastic honeycomb support structure 350 and joincells 400 simultaneously electrically in series using a singleside-mounted cover 420 fitted with mechanical contacts 422 such asspring clips or pin and socket and the like. This lightweight assemblyallows periodic maintenance of cells by dye/electrolyte replacement,double protection against the elements, and removal and replacement offaulty cells in a series array of cells. This is an alternativeconstruction to state-of-the-art thin film solar modules, in which thephotoactive materials are evaporated onto a common conducting support,and in which case individual cell failure may mean irremediable modulefailure.

An additional aspect of the present invention takes advantage of thetransparent or translucent nature of dye cells, a feature unique inphotovoltaic technology. Dye cells are not opaque, like classic siliconor thin film cells, but assume the color of the dye and can betranslucent. Various light transmitting colors are possible, with themost stable being wine colored, and the appearance is aestheticallyattractive. Color matching is possible with building components (e.g.,roof tiles). Cells and modules can be used in roofs, walls, windows,glass curtain walls of buildings and on atriums, stairways and coveredareas (walkways, parking areas, etc.) allowing shade during the day anda pleasing diffuse light, as well as providing power. Such dye cellstructures tend also to filter out the UV component in the transmittedlight, which is a further benefit. The transmissivity of light throughcells can be controlled by such factors as the titania type, the dyetype and dye loading, and are also a function of incident lightwavelength. Practical transmissivities for natural illumination needsare likely to be at least 50% and preferably at least 70%. Of course,the system can be designed with a tradeoff between power productionneeds and illumination needs. Such transparent/translucent dye cells andmodules can also be mounted in place of the normal glass cover of solarwater heaters (i.e., a few centimeters above and parallel to theselective absorber panel). A portion of the incident light is convertedto electricity at up to 10% conversion, but depending on the dye, muchof the remaining light energy can pass through the cell, enabling theremaining light energy to be absorbed by the selective absorber plate ofthe device, thereby providing also thermal energy for water heating (orair space heating). For example, and as shown schematically in FIG. 9a ,a cell module 500 of the present invention is mounted on the face ofsolar water heater 440, so as to provide electricity as well as hotwater from the same basic supporting structural unit and collector area.

It must be emphasized that there is no direct contact between the dyecells and the selective surface/water pipes of the collector, such thatcorrosion and shorts are avoided. The dye and selective coating can alsobe independently optimized to maximize absorption in the blue and redends of the spectrum, respectively. As illustrated in FIG. 9b , dyecells 600 can be fitted onto a tracking or focusing-type solar collector540 (e.g., trough or dish type), provided that the presence of cells 600does not unacceptably reduce transmitted light or distort the optics.(The cells can alternatively be disposed in panel form across the outeredges of the trough or dish, essentially above the collector focus.)This integrated solar system enables direct generation of electricitywithout the need for a turbine. The remaining solar energy, afterpassage through the dye cell, focuses onto the usual receiver pipe 560filled with heat transfer fluid, providing heat generation, for, by wayof example, the provision of steam and hot water for industrial use,space heating, absorption cooling, or seawater desalination usingmultiple-effect distillation. The system can be designed with a tradeoffbetween electrical output and thermal output.

FIG. 10A is a schematic diagram showing the construction of a dye cellthat does not require the use of tin oxide coated glass or plastic. Thecell has a plain glass or plastic upper wall 300 (i.e., the directionfacing the sun), and lower wall 302. The photoanode is an openconducting mesh of titanium 304, part of which is coated with a titanialayer 310. The titania layer, which can be prepared at elevatedtemperatures, is overcoated with a conductive transparent layer of tinoxide 320 by spray, dip, sol gel, vacuum or plasma means. Thecounter-electrode is a similar conducting mesh of titanium 330, part ofwhich is coated with a catalyst layer 340 for the iodine redox reaction,for example graphite powder bonded with a Teflon® binder. The cell alsoincludes a porous separator 345 situated between the two meshes 304 and330. Meshes 304 and 330 pass sealably through a cell perimeter seal 350,which can be of organic or inorganic types, and enable current takeoffoutside the cell. The seal 350 can also include a resealable electrolytefill tube (not shown). The cell is completed by introducing dye into thetitania layer and filling with the redox electrolyte. If necessary, thetitania layer can overcoat mesh 304.

A slight modification of the above construction is shown in FIG. 10B.Titania layer 310 in mesh 304 is now uppermost and has an inertconductive underlayer 315 in intimate contact therewith. In such a case,titania layer 320 can bond directly to the glass if required. Underlayer315 includes a material that is electro-catalytically inert to theiodine redox reaction in the cell, and can be fabricated from an inertconductive ceramic powder (e.g., titanium nitride, tin oxide or magnelioxide powder) bonded by an inert polymer binder such aspolytetrafluoroethylene (Teflon®). If required, the titanium mesh itselfcan be coated with one of these materials to further reduce itsactivity.

FIG. 10C shows two cells in series indicating the facile interconnectionmeans. Mesh 360, emerging from one cell, is the negative terminal of acell 370 and supports a titania layer 365 in the cell. Mesh 368 supportscatalyst in cell 370 and sealably passes through a seal 369, where itsupports a new titania layer 369A in a second cell 375. Mesh 377emerging from cell 375 via a seal 379 is the positive terminal of thetwo-cell construction and supports a catalyst layer 380. It must beemphasized that no external connectors are needed and that both cellspresent a titania electrode to the sun.

As used herein and in the claims section that follows, the term“low-temperature glass” and the like refer to glass that is designed toseal up to the temperature at which titania is processed.

As used herein and in the claims section that follows, the terms “side”and “side wall”, with reference to a photovoltaic cell, refer to a cellwall other than the cell wall that receives the light from the lightsource of the cell. The side wall may be a seal that seals the cell fromthe side, substantially normal to the light emitted by the light source.

As used herein in the specification and in the claims section thatfollows, the term “micron” refers to a micrometer.

As used herein in the specification and in the claims section thatfollows, the term “percent”, or “%”, refers to percent by weight, unlessspecifically indicated otherwise.

Similarly, the term “ratio”, as used herein in the specification and inthe claims section that follows, refers to a weight ratio, unlessspecifically indicated otherwise.

As used herein in the specification and in the claims section thatfollows, the term “largely includes” or “based on”, with respect to acomponent within a formulation or alloy, refers to a weight content ofat least at least 30%, at least 40%, at least 50%, or at least 60% ofthat component.

As used herein in the specification and in the claims section thatfollows, the term “predominantly includes”, with respect to a componentwithin a formulation, refers to a weight content of at least at least50%, at least 65%, at least 75%, or at least 85% of that component.

Throughout this disclosure, various aspects of this invention can bepresented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 10 should be considered to havespecifically disclosed subranges such as from 1 to 2, from 1 to 5, from1 to 8, from 3 to 4, from 3 to 8, from 3 to 10, etc., as well asindividual numbers within that range, for example, 1, 2, 3, 4, 5, 6, 7,8, 9, and 10. This applies regardless of the breadth of the range.

Similarly, the terms “at least”, “exceeds”, and the like, followed by anumber (including a percent or fraction), should be considered to havespecifically disclosed all the possible subranges above that number, aswell as individual numerical values above that number. For example, theterm “at least 75” should be considered to have specifically disclosedsubranges such as 80 and above, 90 and above, etc, as well as individualnumbers such as 85 and 95.

Similarly, the terms “less than”, “below”, and the like, followed by anumber (including a percent, fraction, or ratio such as a weight ratio),should be considered to have specifically disclosed all the possiblesubranges below that number, as well as individual numerical valuesbelow that number. For example, the term “below 75%” should beconsidered to have specifically disclosed subranges such as 70% andbelow, 60% and below, etc, as well as individual numbers such as 65% and50%.

Whenever a numerical range is indicated herein, the range is meant toinclude any cited numeral (fractional or integral) within the indicatedrange. The phrase “ranging/ranges between” a first number and a secondnumber and “within a range of” a first number to a second number, andthe like, are used herein interchangeably and are meant to include thefirst and second indicated numbers and all the fractional and integralnumerals therebetween.

It will be appreciated that certain features of the invention, whichare, for clarity, described in the context of separate embodiments, mayalso be provided in combination in a single embodiment. Conversely,various features of the invention, which are, for brevity, described inthe context of a single embodiment, may also be provided separately orin any suitable sub-combination.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

What is claimed is:
 1. A photovoltaic dye cell for converting a lightsource into an electrical current, the photovoltaic dye cell comprising:(a) a housing for the photovoltaic dye cell, said housing including anat least partially transparent cell wall, said cell wall having a firstinterior surface and a second interior surface; (b) an electrolyte,disposed within said cell wall, between said first and second interiorsurfaces, said electrolyte containing a redox species; (c) an at leastpartially transparent electrically conductive coating, disposed on saidfirst interior surface, within the photovoltaic dye cell; (d) an anodedisposed on said at least partially transparent electrically conductivecoating, said anode including: a porous film, and a dye, absorbed on asurface of said porous film, said dye, said electrolyte, and said porousfilm adapted to convert photons to electrons; (e) a cathode disposedwithin said housing, substantially opposite said anode, and between saidanode and said second interior surface, said cathode having a catalyticsurface facing said anode, said catalytic surface adapted to catalyze aredox reaction of said redox species; (f) a plurality of elongatedelectrically-conductive metallic conductor structures, disposed at leastpartially within the photovoltaic cell, said elongatedelectrically-conductive metallic conductor structures directlycontacting said at least partially transparent electrically conductivecoating and electrically connected with said anode; and (g) a currentcollection element, electrically connected to each of said elongatedelectrically-conductive metallic conductor structures, and configured toremove, via said elongated electrically-conductive metallic conductorstructures, the current produced by the photovoltaic dye cell.
 2. Thephotovoltaic dye cell of claim 1, the photovoltaic dye cell being sealedby an adhesive sealant layer disposed at edges of the photovoltaic dyecell.
 3. The photovoltaic dye cell of claim 1, said cathode including aconductive carbon layer.
 4. The photovoltaic dye cell of claim 1,wherein said redox species is an iodine based redox species.
 5. Thephotovoltaic dye cell of claim 1, said cathode including an electricallyconducting porous mat.
 6. The photovoltaic dye cell of claim 5, saidelectrically conducting porous mat including a carbon fiber veil.
 7. Thephotovoltaic dye cell of claim 5, said electrically conducting porousmat including a titanium mesh.
 8. The photovoltaic dye cell of claim 5,said electrically conducting porous mat including a coating includingcarbon.
 9. The photovoltaic dye cell of claim 5, said electricallyconducting porous mat including a coating including graphite.
 10. Thephotovoltaic dye cell of claim 1, wherein each of said elongatedelectrically-conductive metallic conductor structures includes a metalstrip.
 11. The photovoltaic dye cell of claim 1, wherein each of saidelongated electrically-conductive metallic conductor structures includesa metal wire.
 12. The photovoltaic dye cell of claim 1, wherein saidfirst interior surface and said second interior surface are made of aglass.
 13. The photovoltaic dye cell of claim 1, wherein at least one ofsaid first interior surface and said second interior surface is made ofa glass.
 14. The photovoltaic dye cell of claim 1, wherein at least oneof said first interior surface and said second interior surface is madeof a plastic.
 15. The photovoltaic dye cell of claim 1, wherein at leastone of said first and second interior surfaces includes a tin oxidecoated glass.
 16. The photovoltaic dye cell of claim 1, wherein saidcatalytic surface includes platinum.
 17. The photovoltaic dye cell ofclaim 13, wherein each of said elongated electrically-conductivemetallic conductor structures includes a metal strip.
 18. Thephotovoltaic dye cell of claim 13, wherein each of said elongatedelectrically-conductive metallic conductor structures includes a metalwire.
 19. The photovoltaic dye cell of claim 18, wherein said catalyticsurface includes platinum.
 20. The photovoltaic dye cell of claim 12,wherein each of said elongated electrically-conductive metallicconductor structures includes a metal wire.